1. Field of the Invention
The present invention relates generally to improvements in protective devices, and, more particularly, but not by way of limitation, to improvements in guards for protecting downhole pump power and control cables in the passage of the cables by couplings between tubes of a tubing string extending down a bore hole to the pump.
2. Brief Description of the Prior Art
As is well known in the art, the standard practice in the drilling of an oil well has been to locate a drilling rig on the earth's surface directly above an oil deposit and drill directly downwardly from the surface into the deposit. Oil can then be recovered using a downhole mechanical pump that is operated via a string of sucker rods by a pump jack at the well head.
However, in some circumstances, such an approach cannot be utilized; for example, manmade or natural obstacles may interfere with the positioning of drilling equipment directly above the deposit. In such cases, the deposit can be reached using so-called directional drilling in which the bore hole is caused to follow a curving path to the deposit from a location that may be some horizontal distance from the deposit. Oil is subsequently recovered using a downhole, electrically operated pump that is mounted on the end of a tubing string that extends from the well head into the deposit.
While directional drilling and electrical pumping have permitted the recovery of oil from deposits which could not otherwise be reached and, moreover, has permitted more efficient recovery of oil, they have also given rise to a problem which is not encountered in wells that extend directly downwardly from the surface. Electrical power used to operate the downhole pump is supplied via power cables that extend along the tubing string from the earth's surface to the pump and these cables, as well as electrical control cables, can be damaged in the process of inserting the tubing string into the well. In particular, the tubing string is comprised of a series of tubes that are connected together by couplings which have outside diameters that exceed the diameters of the tubes and these couplings engage the well casing in following the curved path to the oil deposit. If an electrical cable is caught between a coupling and the casing, it will be subjected to crushing and abrasion that can cause breakage of electrical conductors within the cable. Since the pump must be removed from the well any time servicing or repair of the pump is required and then reintroduced into the well, the problem can potentially occur at any of a number of occasions during the productive lifetime of a well.
While electrical cables used in the operation of a downhole pump are commonly armored to minimize the problem of damage to the cables, armoring has not proved to be an adequate solution to the problem. Consequently, it has been proposed that cable guards, mountable on the couplings and having internal channels for passing the cables past the couplings, be provided for protecting those portions of the cables at which damage is likely to occur; that is, portions of the cables positioned alongside the couplings. More particularly, the cable guards would be comprised of a base, extendable about one side of the coupling and including channels for the cables in surfaces of the base that engage the coupling, and a clamp member that is hinged to the base, along one side of the guard, and extends about the opposite side of the coupling. Bolts can then be used to connect distal portions of the clamp member to the base so as to rigidly secure the guard about the coupling.
While the use of such guards has the potential of providing a complete solution to the problem of electrical cable damage, the use of such guards presents problems in its own right. In order that a cable guard be capable of carrying out its function of protecting an electrical cable in the passage of the cable about a tubing coupling, the guard must have a substantial construction. Consequently, since several hundred guards can be required for a single well, the use of such guards would not be an inconsequential expense in the production of oil even though the guards would be reusable. Wear occasioned by movement of a guard along a well casing each time it is mounted on a tubing string, whether in the same or a different well, can eventually lead to breakage that will require replacement of the guard. Similarly, because of the number of guards required to protect the cables in a single well, labor costs associated with the installation of the guards on a tubing string can unduly increase expenses of oil well operation.